1. Field of the Invention
This invention relates to a pulverizer, and more particularly to a pulverizer for use in subjecting resins, pesticides, cosmetics, pigments, and toners to fine particles of micron order.
2. Description of the Prior Art
There are known several types of pulverizers in the art. In term of pulverizing means used in the pulverizer, the pulverizer is classified as follows:
a) Pulverizer using impact force (e.g. hammer mill, impeller breaker, etc.);
b) Pulverizer using grinding and/or compression force (e.g. roller mill, tower mill, etc.);
c) Pulverizer using crushing force (e.g. jaw crusher, gyrotary crusher, etc.);
d) Pulverizer using impact and grinding forces (e.g. ball mill, rod mill, etc.); and
e) Pulverizer using impact and shearing forces (e.g. jet mill, jetmizer, etc.).
When determining a certain type of the pulverizer among these pulverizers for use, thermal characteristics of a material to be pulverized must be considered in addition to the pulverization capacity and efficiency of the pulverizer. For example, pulverization of granular thermoplastic resin, cosmetic, and toner generates heat due to a rapid increase in energy on the surface of the material being pulverized, which results in coagulation and consolidation of fine particles thus prepared. Furthermore, the pulverized fine particles are fused to adhere onto functional parts of the pulverizer for effecting the pulverization. Thus, it is impossible to pulverize the granular thermoplastic resin, cosmetic, and toner by the pulverizer which uses impact, grinding, crushing and compression forces. The preparation of a fine particle of such a material is generally made by the pulverizer using the impact and shearing forces, such as, for example, a jet mill and a jetmizer, because a large amount of compressed cooling gas or low temperature liquid for cooling the particle can be introduced into such a pulverizer.
FIG. 1 shows a conventional pulverizer of the jet mill type, and FIG. 2(a) and 2(b) show a collision member used in the pulverizer shown in FIG. 1.
The conventional pulverizer shown in FIG. 1 includes a casing 1 in which a pulverization chamber 2 is defined. The casing 1 is formed on one side wall thereof with an injection nozzle 3 for injecting a jet B into the pulverization chamber 2. Also, the casing 1 is formed at the portion of the side wall thereof adjacent to the injection nozzle 3 with a supply port for introducing a material A to be pulverized into the pulverization chamber 2. In the casing 1, a collision member 8 is arranged. The collision member is fixedly mounted on a fixing member 6 to be opposite to the injection nozzle 3 so that the material A, which is supplied to the pulverization chamber 2 while being carried on the jet B, may collide with the collision member 8, for pulverization. Also, the casing 1 is formed therein an annular discharge passage 7. The discharge passage is defined between the inner surface of the casing 1 and the periphery of the collision member 8 and fixing member 6 so as to guide the material A which has been pulverized therethrough to a collector (not shown).
As shown in FIGS. 2(a) and 2(b), the collision member 8 incorporated in the conventional pulverizer is formed into a disc-like shape and provided with a pulverization surface 8a which is flat circular in shape and is arranged so as to be perpendicular to the direction of injection of the jet B. When pulverizing the material A using the collision member 8 shown in FIG. 2(a), the whole material A to be pulverized which is introduced through the supply port 4 into the pulverization chamber 2 and carried on the jet B collides directly with the flat circular pulverization surface 8a which is positioned in perpendicular to the direction of the jet B.
However, the collision member 8 having the flat circular pulverization surface 8a shown in FIG. 2(a) causes the material for pulverization to impinge upon the pulverization surface 8a at an angle of 90 degrees in relation to the direction of injection of the jet B, which becomes the impact force of the material against the pulverization surface maximum. As a result, a back pressure is produced at the central portion of the pulverization surface 8a in proportion to both the velocity of the jet B injected straight into the pulverization chamber 2 and the project section of the flat circular pulverization surface 8a, and the impact force of the material A against the pulverization surface 8a is significantly decreased at the central portion of the pulverization surface 8a. Furthermore, the jet B as well as the material A contained in the jet B turn aside without impinging upon the pulverization surface 8a due to interference of the back pressure. Accordingly, the pulverization efficiency of the material, and also the throughput capability of the pulverizer are significantly decreased in the conventional pulverizer shown in FIG. 1.